The overall objective of this proposal is to define the role of estrogen-induced uterine and kidney derived growth factors in the proliferation of rat pituitary tumor cells in vivo and in vitro. The rat pituitary tumor cell line to be used in these studies was established by this laboratory as a subclone of the original GH3 cell population. Our studies with the GH3/C14 cell line have shown that estrogens are required for optimal growth in vivo, but are not capable of promoting continuous growth of these cells in vitro. We have condsidered several possible explanations for these observations in culture, however, our most recent approach has been to ask whether the mitogenic role of estrogens in vivo may be mediated by steroid hormone control of the production and secretion of growth factors specific for the hormone-responsive pituitary tumor cells. To evaluate the possibility of a mediated mechanism involving estrogen-induced polypeptide growth factors, we first prepared extracts of tissues removed from estrogen-treated and estrogen-deficient animals and assayed for growth activity by addition of extracts to cells in serum free medium. Our experiments demonstrate that estrogens elevate the levels of growth factors for GH3/C14 pituitary cells in extracts of both rat uterine and rat kidney tissue. These extracts promote growth of another cell type which also forms hormone-responseive tumors (MTW9/PL rat mammary tumor cells) in appropriate hosts, but do not promote growth of such non-estrogen related cells as 3T3 mouse fibroblasts. Other experiments have identified GH3/C14 cell growth factor activity in estrogen-induced uterine luminal fluid secretions, suggesting that this activity can reach an extracellular compartment and, therefore, may be capable of reaching the general circulation. To date, our experiments suggest a model of hormone-responsive pituitary tumor growth in vivo which includes the mechanism ESTROGENS affect UTERUS AND KIDNEY producing SPECIFIC POLYPEPTIDE GROWTH FACTORS producing ESTROGEN-RESPONSIVE TUMOR CELLS.